Tamsulosin vs Doxazosin switch?

If you stop taking Doxazosin abruptly it may make your condition worse. Your Dr. must give you a discontinuation schedule in order to stop this medication safely and start with Tamsulosin properly. As both of the medications are prescription only your Dr. is responsible for helping you make the transition with the less risks involved to you.

These meds interact moderately meaning:

Interactions between your drugs
Moderate
doxazosin tamsulosin
Applies to: doxazosin, tamsulosin

Using Doxazosin together with Tamsulosin is not recommended. Combining these medications may cause blood pressure to fall excessively and heart rate to increase, especially when you rise from a sitting or lying position. The risk of other side effects such as dizziness, lightheadedness, fainting, headache, flushing, nasal congestion, heart palpitations, and priapism (prolonged and painful erection unrelated to sexual activity) may also increase. These side effects can occur with either medication alone and are most likely to be seen at the beginning of treatment, following a dose increase, or when treatment is restarted after an interruption. Let your doctor know if you develop these symptoms and they do not go away on their own or they become troublesome. Avoid driving or operating hazardous machinery until you know how the medication affects you, and use caution when getting up from a sitting or lying position. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Moderate
Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.

Source: https://www.drugs.com/interactions-check.php?drug_list=934-0,2146-0